1. Field of the Invention
The present invention relates to methods for using adhesive materials to secure two or more semiconductor device components to one another. Particularly, the present invention relates to the use of pressure-sensitive adhesive materials to secure semiconductor device components to each other. The present invention also relates to assemblies including semiconductor device components that are secured to one another with adhesive materials that include a pressure-sensitive component with sufficient bonding strength to at least temporarily secure the semiconductor device components to one another and a thermoset component for more permanently securing the semiconductor device components to one another.
2. State of the Art
Adhesives for Securing Components of Semiconductor Device Assemblies and Packages
Adhesives have long been used to secure the various components of semiconductor device packages or assemblies to one another. Conventionally, thermoset adhesive materials have been used due to their bonding strengths when cured.
The most common conventional methods for attaching a semiconductor die to an interposer, lead frame, printed circuit board, tape, or other carrier include use of thermoset adhesive materials in the form of liquids, pastes, preformed structures, or on adhesive tapes or other elastomeric films. When cured, thermoset adhesive materials have high bond and cohesive strengths, which are desirable for securing the components of a semiconductor device assembly or package to one another so as to prevent movement of these components relative to one another and the possible damage that may be caused to intermediate conductive elements, such as wire bonds, or to the components themselves as a result of such movement.
The types of thermoset adhesive materials that have been used to secure the components of semiconductor device assemblies to one another include conventional thermoset adhesives, so-called xe2x80x9cB-stagexe2x80x9d epoxies, and so-called xe2x80x9csnap curexe2x80x9d epoxies.
Conventional thermoset adhesives have very low bond strengths prior to being cured. Due to these poor bonding strengths, unless the semiconductor device components that are being secured to one another are physically held in place relative to one another, one or both of the semiconductor device components may shift position relative to the other, resulting in misalignment of the semiconductor device components. In addition, conventional thermoset adhesives that are used to secure semiconductor device components in assembled relationships are typically cured by exposure to relatively high temperatures for relatively long periods of time. The temperatures and exposure times that are required to cure many conventional thermoset adhesive materials may damage features on the semiconductor device components, such as by inducing thermal stresses therein, by causing thermal mismatching either before or after curing, by oxidizing features of the components, or otherwise. Moreover, once conventional thermoset adhesives have been cured, the assembled semiconductive device components cannot be removed from one another or repositioned relative to one another.
Snap cure epoxies are similar to conventional thermoset resins in that they have low bond strengths prior to curing and, once cured, the semiconductor device components secured thereby cannot be removed from each other or repositioned relative to each other. The cure times of snap cure epoxies are, however, very short (minutes or even seconds) relative to the cure times of conventional epoxies. While snap cure epoxies cure more quickly than conventional thermoset epoxies, the cure temperatures remain high (e.g., about 200xc2x0 C. to about 225xc2x0 C.) and may cause damage to features on the semiconductor device components.
B-stage epoxies are materials that become tacky after a first, partial cure, imparting these materials with pressure-sensitive adhesive characteristics that are sufficient to temporarily hold the semiconductor device components being secured together in place relative to one another until the B-stage epoxy has been fully cured. Partially cured B-stage epoxies also facilitate the removal of one semiconductor device component from another, as well as repositioning of the semiconductor device components relative to one another. The first, partial cure of B-stage epoxy is typically effected after application thereof to one of the semiconductor device components, but prior to assembling that component with another semiconductor device component. The presence of partially cured, tacky B-stage epoxy on an unassembled semiconductor device component is somewhat undesirable since material particles may adhere thereto, resulting in contamination and possibly in the failure of an assembly or package including the semiconductor device component.
Pressure-sensitive adhesives, which typically function at room temperature, have poor bonding strengths and low cohesive strengths when compared with the thermoset adhesive materials that have conventionally been used to secure the components of semiconductor device assemblies or packages to one another. Consequently, pressure-sensitive adhesive materials are typically not used to permanently secure the components of semiconductor device assemblies or packages to one another. Rather, pressure-sensitive adhesives have been used to temporarily secure the components of semiconductor device assemblies until a more permanent means of securing can be used, such as encapsulating the assemblies in a packaging material.
The art does not teach a method that includes use of an adhesive material to at least temporarily secure the components of a semiconductor device assembly or package to one another at ambient temperature and subsequently curing the adhesive material at a relatively low cure temperature for a short period of time. Nor does the art teach semiconductor device assemblies or packages including components secured to one another with such adhesive materials.
Hybrid Adhesive Materials
Recently, a new class of hybrid adhesive material has been developed. These hybrid adhesive materials have a pressure-sensitive component and a thermosetting component. Exemplary hybrid adhesives of this type are available from 3M as Structural Bonding Tape 9244, Structural Bonding Tape 9245, and Structural Bonding Tape 9246, each of which includes an acrylic pressure-sensitive component and an epoxy thermoset component.
At room temperature, due to their pressure-sensitive adhesive components, these hybrid adhesive materials function as conventional pressure-sensitive adhesives. The bond strengths of these hybrid adhesive materials at room temperature are sufficient to temporarily secure two objects to one another. A more permanent bond between the two objects may be formed by subjecting these hybrid adhesive materials to an increased temperature, which cures the thermoset adhesive components thereof.
While these hybrid materials have been used in place of rivets, spot welds, liquid adhesives, and other permanent fasteners that are used in structural applications for large-dimensional components or objects being fabricated, they have not been used to temporarily or permanently secure the components of semiconductor device assemblies or packages to one another.
The present invention includes a method for at least temporarily securing the components of a semiconductor device assembly or package to one another at room temperature with a hybrid adhesive material. A more permanent bond between the components may subsequently be formed by exposing at least the hybrid adhesive material to a relatively low increased temperature for a relatively short period of time.
A hybrid adhesive material that includes at least a pressure-sensitive component and a thermoset component may be used to effect the method of the present invention. As an example, the pressure-sensitive component of a hybrid adhesive useful in the method and assemblies of the present invention may comprise an acrylic adhesive material, while the thermosetting component may comprise an epoxy thermosetting adhesive material. Examples of such hybrid adhesive materials include those available from 3M as Structural Bonding Tape 9244, Structural Bonding Tape 9245, and Structural Bonding Tape 9246, each of which includes an acrylic pressure-sensitive component and an epoxy thermoset component. At room temperature, due to their pressure-sensitive components, these hybrid adhesive materials function as conventional pressure-sensitive adhesives. At increased temperatures as low as about 120xc2x0 C. or less, the thermoset components of these hybrid adhesive materials cure, or set, providing a more permanent bond between adhered objects.
In use according to the present invention, the hybrid adhesive material is disposed between components of a semiconductor device assembly or package that have been aligned and that are to be secured to one another. The pressure-sensitive component of the hybrid adhesive material facilitates the formation of at least a temporary bond between the semiconductor device components at an ambient temperature, such as room temperature.
Once the semiconductor device components have been assembled and at least temporarily secured to one another with the hybrid adhesive material, the hybrid adhesive material may be subjected to an increased cure temperature for a predetermined period of time so as to cure the thermoset component of the hybrid adhesive material and to provide a more permanent, more secure bond between the semiconductor device components. Preferably, the cure temperature is sufficiently low and cure time sufficiently short so as to not substantially damage or induce thermal stresses on any of the assembled semiconductor device components. For example, the 3M hybrid adhesive materials may be cured, or set, by exposing same to a temperature of about 120xc2x0 C. for about 95 minutes. Of course, higher cure temperatures may alternatively be used for shorter durations to cure the 3M hybrid adhesive materials. When cured, these hybrid adhesive materials provide a bond of sufficient strength between the assembled semiconductor device components.
The present invention also includes assemblies of semiconductor device components that include a hybrid adhesive material between at least a portion of two or more of the semiconductor device components, as well as semiconductor device packages including such assemblies.
Other features and advantages of the present invention will become apparent to those of skill in the art through consideration of the ensuing description, the accompanying drawings, and the appended claims.